1. Field of the Invention
The present invention relates to a method of assembling a micro-actuator for fine movement of a magnetic head.
2. Description of the Related Art
In recent years, reductions in size and thickness of magnetic disk devices, a kind of external storage device for computers, have been under way and, further, reductions in electric power consumption is requested. In addition, magnetic disk devices with higher recording density and larger capacity are demanded. Larger capacity of the magnetic disk devices can generally be realized by increasing the recording capacity per disk. However, an increase in recording density without changing the diameter of the disk leads to narrower track pitch; accordingly, the technical problem is how accurate the head device for reading and writing data on record tracks is positioned, and a head actuator with good positioning accuracy is desired.
Hitherto, in order to position a head with high accuracy in a magnetic disk device, generally, trials have been made to enhance rigidity of movable portions such as an actuator arm and raise the main resonance point frequency in in-plane directions. However, improvement of resonance point has a limit, and even if the in-plane resonance point of the movable portion can be largely raised, there is still the problem that vibration is generated due to spring characteristics of a bearing supporting the movable portion, resulting in a reduction of positioning accuracy.
As a means for solving the above problems, a so-called two-stage actuator in which a second actuator for following the tracks, namely, a tracking actuator is mounted on the tip of an arm of a head actuator, has been proposed. The tracking actuator is for minutely moving the head provided at a tip end portion of an arm, independently from motions of the head actuator, to achieve tracking of the head. A two-stage actuator in which accurate positioning of the head is accomplished by utilizing laminate type piezoelectric elements as the tracking actuator for the two-stage actuator has been proposed.
For example, two laminate type piezoelectric elements are disposed on both sides of an actuator arm, and a voltage is impressed in such a direction that the piezoelectric element on one side is elongated while the piezoelectric element on the other side shrinks, whereon the head is rotated in the direction of the piezoelectric element shrinking under the impressed voltage. However, in the two-stage actuator utilizing the laminate type piezoelectric element according to the prior art, depolarization of the piezoelectric element occurs due to impression of a voltage in the direction reverse to the polarization direction of the piezoelectric element, exposing of the piezoelectric element to a high-temperature atmosphere, aging or the like; as a result, displacement per unit voltage gradually diminishes. Therefore, there is a problem that when the system is used for a certain long time, a desired stroke cannot be obtained. Furthermore, the two-stage actuator according to the prior art utilizing the laminate type piezoelectric elements has a disadvantage that productivity of the laminate type piezoelectric elements is bad, and high accuracy or precision of outer sizes of the elements is required, leading to high cost.
Two-stage actuators utilizing a shearing type piezoelectric element in place of the laminate type piezoelectric element having the above-mentioned many problems have been proposed in Japanese Patent Laid-open No. Hei 10-293979 and Japanese Patent Laid-open No. Hei 11-31368. A minute moving mechanism for head disclosed in the Japanese Patent Laid-open No. Hei 11-31368 has a three-layer structure in which two shearing type piezoelectric elements having different polarization directions are mounted on an electrode formed at the tip of a head arm, and a head suspension is mounted thereon through a movable member therebetween.
Therefore, this structure has a larger thickness from the head arm to the suspension, as compared with the conventional structure in which the suspension is fitted to the head arm with only a spacer. Thus, the two-stage actuator with the three-layer structure is unsuitable for reduction in thickness of the head actuator. Further, the increased thickness leads to wider distance between disk surfaces, whereby the number of disks mountable in the disk device is decreased, and storage capacity is also decreased as compared with the conventional disk device having the same height.
A minute moving mechanism for head which solves the above-mentioned problems has been proposed by the present applicant. In the invention of the previous application, an actuator base bent in a crank shape is fixed to a tip end portion of an actuator arm. A base electrode, a shearing type piezoelectric element, a movable electrode and a hinge plate are laminated and fixed on the actuator base, and a suspension is fixed to the hinge plate. With the actuator base bent in a crank shape, the top surface of the actuator base and the top surface of the hinge plate can be flush with each other, so that the minute moving mechanism for head utilizing the shearing type piezoelectric element can be made thinner.
In the invention of the previous application, electrical conduction must be provided between the shearing type piezoelectric element and the base electrode and the movable electrode, and, therefore, the base electrode and the movable electrode have been fixed to the piezoelectric element by use of a conductive adhesive. On the other hand, electrical insulation must be kept between the actuator base and the base electrode and between the movable electrode and the hinge plate, and, therefore, fixation between the actuator base and the base electrode and between the movable electrode and the hinge plate has been made by use of an ordinary insulating adhesive.
In the method of producing a micro-actuator using a conductive adhesive and an ordinary insulating adhesive according to the invention of the previous application, it is needed to selectively use the two types of adhesive, which leads to complicated production steps. Further, use of a conductive adhesive may easily be attended by generation of a short-circuit due to a mistake in production process. Thus, it is contemplated to contrive use of a single adhesive by using an insulating adhesive also for adhesion of the electrode and the piezoelectric element. However, where an adhesive is merely applied and cured, an adhesive layer thin enough to obtain electrical connection cannot be formed.
Therefore, a method of applying a pressure at the time of curing the adhesive is contemplated. However, where pressure is merely applied upon each lamination of component parts through an adhesive, the thickness of the adhesive layer on application of pressure is added to the thickness of component parts, so that variations of the thickness of the component parts will come out as large variations of the total thickness. Further, where electrical connection is envisioned, two shearing type piezoelectric elements are mounted on the base electrode, and the difference between the thicknesses of left and right piezoelectric elements may cause variations of the adhesive layer even if they are pressed in the same manner. Furthermore, in the conventional method of assembling a micro-actuator, each micro-actuator has been assembled individually, which is unsuitable for mass production.
Accordingly, it is an object of the present invention to provide a method of assembling a micro-actuator which is suitable for mass production.
In accordance with an aspect of the present invention, there is provided a method of assembling a micro-actuator, comprising the steps of: placing a base frame having a plurality of actuator bases on a stage; applying a first adhesive to each of the actuator bases; placing a base electrode frame having a plurality of base electrode on the first adhesive applied to the base frame; clamping the base frame and the base electrode frame between the stage and a first head, followed by heating for a first predetermined period of time while exerting a predetermined first press load onto the first head to semi-cure the first adhesive; applying a second adhesive to each of the base electrodes; placing a plurality of piezoelectric elements on the second adhesive applied to each of the base electrodes; clamping the base frame, the base electrode frame and the piezoelectric elements between the stage and a second head, followed by heating for a second predetermined period of time while exerting a predetermined second press load onto the second head to semi-cure the second adhesive; applying a third adhesive to the piezoelectric elements; placing a movable electrode frame having a plurality of movable electrodes on the third adhesive applied to each of the piezoelectric elements; clamping the base frame, the base electrode frame, the piezoelectric elements and the movable electrode frame between the stage and a third head, followed by heating for a third predetermined period of time while exerting a predetermined third press load onto the third head to semi-cure the third adhesive; applying a fourth adhesive to each of the movable electrodes; placing a hinge plate frame having a plurality of hinge plates on the fourth adhesive applied to each of the movable electrodes; and clamping the base frame, the base electrode frame, the piezoelectric elements, the movable electrode frame and the hinge plate frame between the stage and a fourth head, followed by heating for a fourth predetermined period of time while exerting a predetermined fourth press load onto the fourth head to semi-cure the fourth adhesive.
Preferably, the stage has a plurality of positioning pins, whereas the base frame, the base electrode frame, the movable electrode frame and the hinge plate frame respectively have a plurality of positioning holes. The base frame, the base electrode frame, the movable electrode frame and the hinge plate frame are mounted on the stage while being relatively positioned by insertion of the positioning pins in the positioning holes.
Preferably, the stage includes a work mount portion having a plurality of positioning pins, a predetermined height from a bottom surface of the stage and a predetermined size. The base frame, the base electrode frame, the movable electrode frame and the hinge plate frame are once mounted on a holder having an opening larger than the size of the work mount portion, before being placed on the work mount portion of the stage.
A method of assembling a micro-actuator according to the present invention further comprises a step of heating the adhered laminate at a predetermined temperature for a fifth predetermined period of time to fully cure the first to fourth adhesives. Each of the actuator bases, each of the base electrodes, each of the movable electrodes and each of the hinge plates are connected respectively to the base frame, the base electrode frame, the movable electrode frame and the hinge plate frame by, a bridge. A method of assembling a micro-actuator according to the invention further comprises a step of cutting each of the bridges of the base electrode frame, the movable electrode frame and the hinge plate frame after the step of fully curing the adhesives.
In accordance with another aspect of the present invention, there is provided a method of assembling a micro-actuator, comprising the steps of: placing a base frame having a plurality of actuator bases on a stage; applying a first adhesive to each of the actuator bases; placing a base electrode frame having a plurality of base electrodes on the first adhesive applied to the base frame; clamping the base frame and the base electrode frame between the stage and a first head, followed by heating for a first predetermined period of time while exerting a predetermined first press load onto the first head to semi-cure the first adhesive; applying a second adhesive to each of the base electrodes; placing a plurality of piezoelectric elements on the second adhesive applied to each of the base electrodes; clamping the base frame, the base electrode frame and the piezoelectric elements between the stage and a second head, followed by heating for a second predetermined period of time while exerting a predetermined second press load onto the second head to semi-cure the second adhesive; applying a third adhesive to the piezoelectric elements; placing a hinge plate frame having a plurality of hinge plates on the third adhesive applied to each of the piezoelectric elements; and clamping the base frame, the base electrode frame, the piezoelectric elements and the hinge plate frame between the stage and a third head, followed by heating for a third predetermined period of time while exerting a predetermined third press load onto the third head to semi-cure the third adhesive.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.